1. Technical Field
The embodiments herein generally relate to wireless communications systems, and, more particularly, to enhanced packet modes in Digital Audio Broadcasting-Internet Protocol (DAB-IP) systems.
2. Description of the Related Art
At the transmitter side of a wireless communications system, service component data content (IP datagrams) can be structured into Main Service Channel (MSC) data groups for transport in one or more data packets. An MSC data group contains a data group header, a data group data field, and an optional data group Cyclic Redundancy Check (CRC). The information associated with one MSC data group is transmitted in one or more data packets, sharing the same address. All packets may contain padding bytes. FIG. 1 shows the situation when a MSC data group is spread across several packets, sharing the same address.
Forward Error Correction (FEC), in the form of Reed Solomon (RS) outer error protection and outer interleaving, can be applied to sub-channels carrying service components in a packet mode in order to further increase the error robustness of DAB data delivery. In this context, error robustness refers to the fact that the receiver will be able to correct more errors (i.e., the RX can operate under small signal to noise ratio). FIG. 2 shows the structure of a FEC frame 50. The frame has the dimensions of 204 columns by 12 rows and includes an Application Data Table of 188 columns by 12 rows (i.e., 2,256 bytes) and an RS Data Table of 16 columns by 12 rows (i.e., 192 bytes).
Data packets are fed into the Application Data Table. The RS Data Table is filled by calculating the RS codeword from each row of data. The RS Data Table is transported within nine consecutive FEC packets. The set of FEC packets is transmitted immediately following the Application Data Packet Set used to form the Application Data Table. The structure of the FEC packets is shown in FIG. 3. The complete set of FEC packets used to transport the RS data is shown in FIG. 4.
At the receiver side of a wireless communications system, the receiver receives the transmitted packets and it must construct the FEC frame and then apply RS decoding on this frame to correct the errors (if any). When the receiver is on, it starts to receive packets. It is not necessary that the first received packet is the first packet in the FEC frame; it may be any packet inside the FEC frame, therefore the receiver cannot begin to build the FEC frame until it receives the first packet in the FEC frame then begins to fill it, thus one must detect the beginning of the FEC frame because if there are any small differences between the transmitted FEC frame and the FEC frame constructed by the receiver using the received packets, then the position of the RS parity bytes will be changed and RS decoder will fail to decode the frame and all of the subsequent frames, thus, all received data will be corrupted. Accordingly, there remains a need for a technique for FEC frame synchronization in DAB-IP systems.